DE102009045306A1 - Method and device for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (2) with several cylinders (3), wherein fuel can be injected into the several cylinders (3) via respective injection valves and air can be admitted via respective inlet valves (9) to create an air-fuel mixture to be formed in the cylinders (3) to provide a drive torque, combustion exhaust gas being able to be discharged from the cylinders (3) via a catalytic converter (6); with the following steps: - Operating the internal combustion engine (2) in a first engine operating mode in which no fuel is injected into at least one first cylinder (3), so that the at least one first cylinder (3) does not contribute to the drive torque, and only fuel is injected into at least one second cylinder (3) in order to provide the drive torque; and - switching to a second engine operating mode in which fuel is injected into the at least one first cylinder (3) and into the at least one second cylinder (3), so that the at least one first cylinder (3) and the at least one second cylinder ( 3) contributes to providing the drive torque; characterized in that when switching to the second engine operating mode, the combustion in the at least one second cylinder (3) is carried out with an excess of air, so that a proportion of the air admitted into the at least one second cylinder (3) with the combustion exhaust gas into the catalytic converter ( 6).

Description

Technical area

The invention relates to a method and a device for operating an internal combustion engine, in particular a method for operating an internal combustion engine in the transition from a partial engine operation to a full engine operation.

State of the art

In direct injection internal combustion engines, particularly in gasoline engines, the internal combustion engine may be operated to reduce the propulsion torque provided in a mode in which a portion of the cylinders are shut off, i. H. is operated so that there is no combustion in it and thus no drive torque is generated in these cylinders. Such an operating mode is called partial engine operation. The mode in which half of the cylinders are turned off is called half engine operation.

When the internal combustion engine is operated in partial engine mode, the intake and exhaust valves for supplying and discharging gases remain closed in the respective deactivated cylinders and the injection is suspended for these cylinders. The shutdown of the respective cylinder takes place at the transition to the partial engine operation immediately after an air-fuel mixture has been burned in the cylinder in question. After combustion, the exhaust valve remains closed, so that the combustion exhaust gases in the cylinder remain there. The combustion engine is powered by the active, d. H. not shut down cylinders driven and provides a corresponding drive torque ready. Thereby, the pistons are moved in the deactivated cylinders, so that the combustion exhaust gas contained therein from the last combustion is successively compressed and expanded.

Between full engine operation, where all cylinders are active, and partial engine operation, where only a portion of the cylinders are active, becomes dependent on an operating point, such as load and / or speed, and / or dependent on an external default , as a driver's request, which can be specified by an accelerator pedal position, switched.

With direct fuel injection, fuel is injected directly into the combustion chamber with the aid of injection valves. Even with closed injectors, it can not be ruled out that leakage fuel will enter the cylinder. For example, with conventional injectors, leakage of up to 2.5 mm ³ per minute is possible and not uncommon. If the internal combustion engine is operated in partial engine mode, the leakage in the deactivated cylinders can lead to fuel entering the combustion chambers of the deactivated cylinders. Thus, the trapped combustion exhaust gas is enriched with unburned fuel. Since the partial engine operation can be taken on average for several minutes, the amount of fuel that has entered the combustion chambers of the deactivated cylinders is not negligible. Once the engine is switched back from the partial engine operation to the full engine operation, the fuel-enriched combustion exhaust gas is discharged into the exhaust system of the internal combustion engine.

Legal requirements, however, set emission limit values for hydrocarbons released into the environment. These specifications are valid for all operating modes, both for full engine operation, partial engine operation, and during the switching phase between the two modes of operation.

In internal combustion engines with direct fuel injection, a catalyst is usually used for improving the exhaust gas to reduce the emission of nitrogen oxides and carbon monoxide. Such a catalyst is capable of storing oxygen to some extent. In a lean mixture, which leads to combustion exhaust gases, in which an air content is included, oxygen is stored in the catalyst. For a rich mixture resulting in combustion exhaust gas containing unburned HC (hydrocarbon) fractions, the catalyst releases the oxygen and oxidizes the unburned hydrocarbon fractions in the combustion exhaust gas.

It is an object of the present invention to provide a method and a device for operating an internal combustion engine in partial engine operation, wherein in particular when switching from partial engine operation to full engine operation, the proportion of unburned hydrocarbons in the combustion exhaust gas entering the environment is reduced or eliminated ,

Disclosure of the invention

This object is achieved by the method for operating an internal combustion engine according to claim 1 and by a corresponding device and an engine system according to the independent claims.

Further advantageous embodiments are specified in the dependent claims.

• – Betreiben des Verbrennungsmotors in einer ersten Motorbetriebsart, bei der in mindestens einen ersten Zylinder kein Kraftstoff eingespritzt wird, so dass der mindestens eine erste Zylinder nicht zu dem Antriebsmoment beiträgt, und nur Kraftstoff in mindestens einen zweiten Zylinder eingespritzt wird, um das Antriebsmoment bereitzustellen; und
• – Umschalten zu einer zweiten Motorbetriebsart, bei der in den mindestens einen ersten Zylinder und in den mindestens einen zweiten Zylinder Kraftstoff eingespritzt wird, so dass der mindestens eine erste Zylinder und der mindestens eine zweite Zylinder zum Bereitstellen des Antriebsmoments beiträgt;

wobei beim Umschalten in die zweite Motorbetriebsart die Verbrennung in dem mindestens einen zweiten Zylinder mit einem Luftüberschuss durchgeführt wird, so dass ein Anteil der in den mindestens einen zweiten Zylinder eingelassenen Luft mit dem Verbrennungsabgas in den Katalysator gelangt.According to a first aspect, a method for operating an internal combustion engine with a plurality of cylinders, wherein fuel is injectable into the plurality of cylinders via respective injectors and air is admitted via respective intake valves to form an air-fuel mixture in the cylinders to provide a drive torque, wherein combustion exhaust gas from the cylinders is dischargeable via a catalyst. The method comprises the following steps:

• Operating the internal combustion engine in a first engine mode in which no fuel is injected into at least one first cylinder such that the at least one first cylinder does not contribute to the drive torque and only fuel is injected into at least one second cylinder to provide the drive torque; and
• Switching to a second engine mode in which fuel is injected into the at least one first cylinder and the at least one second cylinder so that the at least one first cylinder and the at least one second cylinder contribute to providing the drive torque;

wherein when switching to the second engine mode, the combustion in the at least one second cylinder is performed with an excess of air, so that a proportion of the recessed into the at least one second cylinder air with the combustion exhaust gas enters the catalyst.

According to one embodiment, when switching to the second engine mode, combustion exhaust gas may be expelled from a last combustion from the at least one first cylinder, the combustion being performed in the at least one second cylinder with excess air, such that the proportion of the at least one second cylinder admitted air with the combustion exhaust gas before or simultaneously with the combustion exhaust gas of the last combustion passes from the at least one first cylinder in the catalyst.

An idea of the above method is that before, during and immediately after switching from a first engine operating mode, in particular a partial engine operation, to a second engine operating mode, in particular full engine operation, the consequences of the leakage of a closed injection valve of the cylinder switched off in partial engine operation are compensated. in advance by providing the catalyst with oxygen which can accumulate there. When the leakage fuel-enriched combustion exhaust gas is exhausted when opening the exhaust valve of the inactive cylinder into the exhaust gas portion, the hydrocarbons in the combustion exhaust gas may be oxidized as it flows through the catalyst and the hydrocarbon components in the exhaust gas are reduced or eliminated. Alternatively or additionally, it is possible to supply the additional atmospheric oxygen to the second cylinders so that they arrive at the same time as the unburned leakage fuel from the first cylinders to the catalyst, so that the leakage fuel can be oxidized there. The atmospheric oxygen is provided by operating the engine in partial engine operation prior to switching to full engine operation with a lean mixture in which the air fraction is greater than necessary for complete combustion of the injected fuel.

Further, the combustion in the at least one second cylinder may be performed with the excess air when a switching condition for switching to the second engine mode is satisfied.

According to one embodiment, an amount of fuel that has entered the at least one first cylinder through leakage of the respective injectors into combustion chambers of the at least one first cylinder during a first engine operating mode can be determined, in particular by means of a leakage function that measures the amount of fuel into the cylinders penetrating fuel depending on operating variables, in particular the rotational speed and / or a pressure in the fuel supply to the injection valve describes.

According to one embodiment, the amount of fuel that has entered the at least one first cylinder during the first engine mode by leakage of the respective injectors into combustion chambers of the at least one first cylinder, depending on a leakage value indicating the amount of fuel infiltrating per unit time can be determined.

Further, a leaning period during which the combustion is performed in the at least one second cylinder with the excess air and a degree of the excess air may be selected depending on the determined amount of fuel.

• – Ermitteln einer in dem Katalysator gespeicherten Luftmenge mit Hilfe einer vorgegebenen Katalysator-Funktion;
• – Betreiben des Verbrennungsmotors vor dem Umschalten in die zweite Motorbetriebsart mit dem Luftüberschuss, wobei eine Abmagerungs-Zeitdauer, während der die Verbrennung in dem mindestens einen zweiten Zylinder mit dem Luftüberschuss durchgeführt wird, und ein Grad des Luftüberschusses abhängig von der in dem Katalysator gespeicherten Luftmenge gewählt sind.

It can be provided that the method comprises the further steps:

• - Determining an amount of air stored in the catalyst by means of a predetermined catalyst function;
• - Operating the internal combustion engine before switching to the second engine mode with the excess air, wherein a leaning period during which the combustion is performed in the at least one second cylinder with the excess air, and a degree of excess air depending on the amount of air stored in the catalyst are selected.

In particular, the amount of air stored in the catalyst may be determined depending on one or more of the exhaust gas mass flow through the catalyst, a lambda value upstream of the catalyst, a lambda value downstream of the catalyst, and a temperature of the catalyst.

• – den Verbrennungsmotor in einer ersten Motorbetriebsart zu betreiben, bei der in mindestens einen ersten Zylinder kein Kraftstoff eingespritzt wird, so dass der mindestens eine erste Zylinder nicht zu dem Antriebsmoment beiträgt, und nur Kraftstoff in mindestens einen zweiten Zylinder eingespritzt wird, um das Antriebsmoment bereitzustellen; und
• – auf eine zweite Motorbetriebsart umzuschalten, bei dem in alle Zylinder Kraftstoff eingespritzt wird, so dass jeder der Zylinder zum Bereitstellen des Antriebsmoments beiträgt;

wobei das Steuergerät weiterhin ausgebildet ist, um beim Umschalten in die zweite Motorbetriebsart die Verbrennung in dem mindestens einen zweiten Zylinder mit einem Luftüberschuss durchzuführen, so dass ein Anteil der in den mindestens einen zweiten Zylinder eingelassenen Luft mit dem Verbrennungsabgas in den Katalysator gelangt.According to a further aspect, there is provided a controller for operating a multi-cylinder internal combustion engine, wherein fuel is injectable into the plurality of cylinders of the internal combustion engine via respective injectors and air is admitted via respective intake valves to produce an air-fuel mixture in the cylinders to provide a drive torque form, wherein combustion exhaust gas from the cylinders via a catalyst can be discharged;
wherein the controller is adapted to

• To operate the engine in a first engine mode in which no fuel is injected into at least one first cylinder such that the at least one first cylinder does not contribute to the drive torque and only fuel is injected into at least one second cylinder to provide the drive torque ; and
• To switch to a second engine mode in which fuel is injected into all cylinders so that each of the cylinders contributes to providing the drive torque;

wherein the controller is further configured to perform the combustion in the at least one second cylinder with an excess of air when switching to the second engine mode, so that a proportion of the recessed into the at least one second cylinder air with the combustion exhaust gas enters the catalyst.

According to another aspect, there is provided an engine system including the above controller and a multi-cylinder engine, the cylinders each having an injector for injecting fuel into the plurality of cylinders of the engine and intake valves for injecting air into the cylinders to provide airflow. Form fuel mixture in the cylinders to provide a driving torque, wherein a catalyst is provided, is discharged through the combustion exhaust gas from the cylinders.

Brief description of the drawings

Preferred embodiments will be explained in more detail with reference to the accompanying drawings. Show it:

1 a schematic representation of an engine system in which the method for switching from the partial engine operation to the full engine operation can be performed;

2 a flowchart for illustrating the method for switching between the partial engine operation and the full engine operation.

Description of embodiments

In 1 is an engine system 1 with an internal combustion engine 2 shown. The internal combustion engine 2 is preferably a gasoline engine with direct fuel injection. The internal combustion engine 2 includes four cylinders in the illustrated embodiment 3 , Fuel is delivered via injectors 7 in the cylinders 3 injected. The injectors 7 stand with a fuel line 8th in connection, in the fuel to each of the cylinders 3 to be led.

The cylinders 3 Air is supplied via an air supply section 4 fed. To air in the cylinder 3 let in is for each of the cylinders 3 an inlet valve 9 intended. The combustion exhaust gas is via exhaust valves 11 out of the cylinder 3 ejected and via a Abgasabführungsabschnitt 5 dissipated. In the exhaust discharge section 5 is a catalyst 6 which can convert, inter alia, carbon monoxide and nitrogen oxides.

It is also a control unit 10 provided that with actuators of the internal combustion engine 2 in the air supply section 4 and in the exhaust discharge section 5 connected to this in an appropriate manner for operating the internal combustion engine 2 head for. In detail, the controller controls 10 the injectors 7 , the intake valves 9 , the exhaust valves 11 and other actuators or actuators of the engine system. Furthermore, in the engine system 1 suitable sensors, such. Example, a lambda probe, one or more temperature sensors, pressure sensors and the like provided to detect engine conditions, so that the operation of the internal combustion engine 2 can be performed depending on the existing engine conditions.

The control unit 10 controls the internal combustion engine 2 to provide a drive torque. For this receives the control unit 10 external request signals E, such as a driver's desired torque, an accelerator pedal position and the like, with which a drive torque request can be specified externally. Furthermore, the controller receives 10 from the sensors corresponding information about engine conditions, such. As the speed, pressures and temperatures in the air supply section 4 and / or in the Abgasabführungsabschnitt 5 ,

In normal operation, all cylinders 3 of the internal combustion engine 2 active and will be in accordance with Four-stroke operation operated. That is, in each of the cylinders 3 a sequence of work cycles is executed. This is how each of the cylinders performs 3 cyclically a sequence of a compression stroke, in the air-fuel mixture in the cylinder 3 by a movement of a piston in the cylinder 3 is compressed, a combustion cycle in which the combustion in the cylinder 3 takes place and the combustion chamber by a movement of the piston in the cylinder 3 expands, an exhaust stroke, where the combustion exhaust gases from the cylinder 3 in the Abgasabführungsabschnitt 5 are discharged, and an intake stroke, while the air through the air supply section 4 in the cylinder 3 is sucked. The cylinders 3 perform these work cycles offset from each other.

Depending on the desired operating state, for example specification of a driver's desired torque or operating state of the internal combustion engine 2 , such as idling, the control unit can 10 decide that the drive torque of only a part of the cylinder 3 should be provided. In this case, a first group of cylinders is turned off and the total drive torque provided by a second group of active cylinders. Will be half the cylinder 3 switched off, it is called a half-engine operation. Half-engine operation represents the standard of partial engine operation, since this is the mechanics of the internal combustion engine 2 least burdened.

When switching off the cylinders 3 the first group will, after a final combustion in one of these cylinders 3 has been carried out, the relevant outlet valve 11 not open so that the combustion gases in the cylinder in question 3 remain. The drive torque, the still active cylinder through the second group 3 is provided moves the pistons in the cylinders 3 the first group, so that there the combustion exhaust gas is compressed and expanded. The drive torque of the active cylinders 3 the second group is chosen so that the required drive torque of the internal combustion engine 2 including the lost torque of the deactivated cylinders 3 the first group is generated.

When changing the operating conditions or changes in the specification of the driver's desired torque, the control unit 10 notice that now should be switched back from the partial engine operation in the full engine operation. This will be one or more of the cylinders 3 the first group put back into service by first using the exhaust valves 11 the cylinder concerned 3 the combustion exhaust gas is discharged and with the next expansion movement of a piston in the combustion chamber of the respective cylinder 3 Air in the previously inactive cylinder 3 is sucked in to the next cycle by injection of fuel, by compression of the air-fuel mixture in the cylinder 3 and by ignition of the air-fuel mixture again a drive torque through the respective cylinder 3 to provide.

During partial engine operation may be due to the leakage of the injectors 7 When closed, fuel is also in the deactivated cylinders 3 arrive, so that the fuel has penetrated into the combustion chamber mixed with the combustion exhaust gas and there increases the hydrocarbon content. Typical leakage values up to 2.5 mm ³ per minute at a fully closed injection valve 7 , These values are for active cylinders 3 of the internal combustion engine 2 uncritical, since the amount of fuel that enters the cylinder during a power stroke 3 flows in, is negligible and does not significantly affect the quality of the combustion exhaust gas. However, since in partial engine operation, the cylinder 3 of the first group are not active over a longer period of time of up to several minutes, the over the leakage of the injection valve 7 Enrich penetrated fuel. When opening the exhaust valve 11 for restarting one or more of the (deactivated) cylinders 3 The first group thus becomes combustion exhaust gas in the exhaust discharge section 5 omitted, which is highly enriched with hydrocarbons of the penetrated fuel. This degrades the quality of the emissions of the internal combustion engine 2 ,

In 2 1 is a flowchart illustrating a method of switching from a partial engine operation to a full engine operation in which the emission performance is improved over that described above. This method can be analogously applied to cases in which is switched to a further partial engine operation and to a previously inactive cylinder is put back into operation.

In step S1, it is checked whether to switch from a partial engine operation in a full engine operation. This may be in accordance with a switching condition depending on operating conditions of the internal combustion engine 2 , such as load and speed, and / or done depending on a specification of a driver's desired torque. If these are within certain operating ranges, then it can be decided that it should be switched from a partial engine operation in a full engine operation.

If the conditions for switching to full engine operation are fulfilled (alternative: yes), the catalyst will be used 6 stored fuel is calculated (step S2). The calculation of the catalyst 6 stored oxygen is usually carried out with the help of a given catalyst function, the may be predetermined in the form of a functional equation and / or in the form of a catalytic converter characteristic diagram. The predetermined catalyst function may have a lambda value upstream and a lambda value downstream of the catalyst 6 , an exhaust gas mass flow through the catalyst 6 , a temperature of the catalyst 6 and other state variables. The lambda values of the exhaust gas can be determined with the help of lambda sensors, in front of and behind the catalytic converter 6 are arranged to be determined. The lambda values indicate whether that is in the cylinders 3 burned air-fuel mixture is too rich or too lean and by how much the air-fuel mixture with respect to a stoichiometric balance between air and fuel has contained an excess of air or a fuel surplus. With the help of the applied catalyst function can then information about the catalyst in the 6 stored oxygen can be calculated.

In step S3 is now calculated or estimated, which amount of fuel in the cylinder 3 the first group by leakage of the injectors 7 has penetrated and has mixed with the combustion exhaust gas therein. This may be dependent on the length of time during which the engine is running 2 has been operated in partial engine operation, determined or estimated. Furthermore, by measuring the leakage in the internal combustion engine 2 used injection valves 7 Leakage values (fuel quantity / unit time) can be determined, so that the quantity of the into the cylinder 3 the first group of penetrated fuel by multiplying the leakage value of the respective injection valve 7 with the duration of the partial engine operation can be obtained. Other approaches to obtain the amount of fuel in the combustion exhaust gas, such as. B. with an applicable leakage function that can be mapped using a map, are conceivable. In addition, the amount of catalyst in the depends 6 required oxygen also from the number of deactivated cylinders 3 of the first group, as this determines the amount of hydrocarbons entering the combustion exhaust gas.

In step S4 now becomes dependent on that in the catalyst 6 stored amount of oxygen and determined depending on the determined amount of fuel, whether the oxygen content in the catalyst 6 must be increased in the catalyst 6 completely oxidize the fuel. In principle, that must be in the catalyst 6 when switching to full engine operation, the amount of fuel flowing and the amount of stored oxygen form a stoichiometric balance. The stoichiometric equilibrium in gasoline-powered gasoline engines, for example, 1: 14.7, so that the required amount of oxygen can be clearly calculated in knowledge of the fuel content of the exhaust gas emitted at the switching.

If it is determined in step S5 that there is insufficient oxygen in the catalytic converter with respect to the fuel content to be expected in the combustion exhaust gas during the switchover 6 is present (alternative: yes), so now before, during and immediately after switching to the partial engine operation, the cylinder 3 the second group are operated with a lean air-fuel mixture (step S6), in which there is an excess of air. Ie. There is air from the air supply section 4 in the exhaust section 5 passed, ie it is a leaner air-fuel mixture in the cylinders concerned 3 the second group burned. The degree of leaning corresponds to a size which is suitable, a certain proportion of oxygen or a certain amount of oxygen to the catalyst 6 so that it stores the oxygen. The time window in which this leaning is carried out is chosen so that as long as by restarting additional unburned fuel in the catalyst 6 get the cylinders 3 the second group are operated with a leaner air-fuel mixture.

If it is determined in step S5 that the stored oxygen in the catalyst 6 sufficient to one probably in the cylinders 3 to compensate for the amount of fuel or hydrocarbon present in the first group (alternative: no), must be the catalyst 6 before switching to full engine operation, no additional oxygen is supplied and the air-fuel mixture is not emaciated.

In step S7, the changeover to the full engine operation by taking up the power stroke in the cylinders 3 the first group. When switching to the full engine operation is from the cylinders 3 the first group of exhaust gas is ejected so that hydrocarbons pass through the catalyst 6 stream. These combine with the stored oxygen and are thereby oxidized.

In further embodiments, it may alternatively be provided to store as much oxygen as possible in the catalyst. This can be done if the leak value is not known with the fuel on closed injectors 7 in the cylinder 3 penetrates. This can z. B. before switching to full engine operation for a certain period of time, the air-fuel mixture can be provided with a maximum or predefined emptying to those in the catalyst 6 to increase the stored amount of oxygen.

The lean of the air-fuel mixture of step S6 can be withdrawn immediately after switching from partial engine operation to full engine operation again. Alternatively, the weight loss after a certain number of crankshaft revolutions or ignitions can be withdrawn.

Since the amount of oxygen needed to oxidize the hydrocarbons in the combustion exhaust gas is not known, the degree of leanness and the leaning period during which the engine can 2 is operated with a lean air-fuel mixture before switching to the full engine operation, basically also be made directly dependent on how long the engine 2 was operated in partial engine mode. Ie. the degree of leanness and / or the leaning time period prior to performing the switch to full engine operation can be directly determined by means of a suitable function from the duration during which the engine is running 2 has been operated in partial engine mode, and from the number of shut down, then to be put into operation cylinder 3 be determined.

If it is determined in step S5 that the catalyst 6 has stored too little oxygen, so that the emaciation is not sufficient, it can be provided that the switching is delayed from the partial engine operation in the full engine operation until the catalyst 6 has stored enough oxygen.

As already mentioned above, instead of the partial engine operation, it is also possible to switch over to a further partial engine operation. Essential for the above method is that a previously deactivated cylinder is active again after switching, d. H. contributes to providing the drive torque. It is irrelevant whether the number of active cylinders before switching is greater than, equal to or less than the number of active cylinders after switching.

Claims (10)

Method for operating an internal combustion engine ( 2 ) with several cylinders ( 3 ), whereby fuel in the several cylinders ( 3 ) via respective injection valves ( 7 ) injectable and air via respective intake valves ( 9 ) is admitted to an air-fuel mixture in the cylinders ( 3 ) for providing a drive torque, wherein combustion exhaust gas from the cylinders ( 3 ) via a catalyst ( 6 ) is dissipatable; with the following steps: - operating the internal combustion engine ( 2 ) in a first engine mode, in which at least one first cylinder ( 3 ) no fuel is injected, so that the at least one first cylinder ( 3 ) does not contribute to the drive torque, and only fuel into at least one second cylinder ( 3 ) is injected to provide the drive torque; and - switching to a second engine mode, in which in the at least one first cylinder ( 3 ) and in the at least one second cylinder ( 3 ) Fuel is injected so that the at least one first cylinder ( 3 ) and the at least one second cylinder ( 3 ) contributes to providing the drive torque; characterized in that, when switching to the second engine mode, the combustion in the at least one second cylinder ( 3 ) is performed with an excess of air, so that a proportion of the at least one second cylinder ( 3 ) admitted air with the combustion exhaust gas in the catalyst ( 6 ). The method of claim 1, wherein when switching to the second engine mode, combustion exhaust gas from a last combustion is exhausted from the at least one first cylinder. 3 ) is expelled, the combustion in the at least one second cylinder ( 3 ) is performed with an excess of air, so that the proportion of in the at least one second cylinder ( 3 ) with the combustion exhaust gas before or at the same time as the combustion exhaust gas of the last combustion from the at least one first cylinder ( 3 ) in the catalyst ( 6 ). Method according to claim 1 or 2, wherein the combustion in the at least one second cylinder ( 3 ) is performed with the excess air when a switching condition for switching to the second engine mode is satisfied. Method according to one of claims 1 to 3, with the further step: - determining an amount of fuel which during a first engine operating mode in the at least one first cylinder ( 3 ) by leakage of the respective injectors ( 7 ) in combustion chambers of the at least one first cylinder ( 3 ) has penetrated, in particular by means of a leakage function, which measures the quantity of the cylinder ( 3 ) penetrating fuel depending on operating variables, in particular the rotational speed and / or a pressure in the fuel supply to the injection valve ( 7 ), describes. The method of claim 4, wherein the amount of fuel injected into the at least one first cylinder during the first engine mode ( 3 ) by leakage of the respective injectors ( 7 ) in combustion chambers of the at least one first cylinder ( 3 ), depending on a leakage value indicating the amount of fuel entering per unit time is determined. A method according to claim 4 or 5, wherein a leaning period during which the Combustion in the at least one second cylinder ( 3 ) is performed with the excess air, and a degree of excess air can be selected depending on the determined amount of fuel. Method according to one of claims 4 to 6, with the further steps: - determining a in the catalyst ( 6 ) stored air quantity by means of a predetermined catalyst function; - operating the internal combustion engine ( 2 ) before switching to the second engine mode with the excess air, wherein a leaning period during which the combustion in the at least one second cylinder ( 3 ) is performed with the excess air, and a degree of excess air depending on the in the catalyst ( 6 ) stored air quantity are selected. Process according to claim 7, wherein in the catalyst ( 6 ) is determined as a function of one or more of the following parameters: an exhaust gas mass flow through the catalytic converter ( 6 ), a lambda value upstream of the catalyst, a lambda value downstream of the catalyst ( 6 ) and a temperature of the catalyst. Control unit ( 10 ) for operating an internal combustion engine ( 2 ) with several cylinders ( 3 ), whereby fuel in the several cylinders ( 3 ) of the internal combustion engine via respective injection valves ( 7 ) injectable and air via respective intake valves ( 9 ) is admitted to an air-fuel mixture in the cylinders ( 3 ) for providing a drive torque, wherein combustion exhaust gas from the cylinders ( 3 ) via a catalyst ( 6 ) is dissipatable; whereby the control unit ( 10 ) is designed to - the internal combustion engine ( 2 ) in a first engine mode, in which at least one first cylinder ( 3 ) no fuel is injected, so that the at least one first cylinder ( 3 ) does not contribute to the drive torque, and only fuel into at least one second cylinder ( 3 ) is injected to provide the drive torque; and - to switch to a second engine mode in which all cylinders ( 3 ) Fuel is injected so that each of the cylinders ( 3 ) contributes to providing the drive torque; characterized in that the control unit ( 10 ) is further configured to switch combustion in the at least one second cylinder when switching to the second engine mode ( 3 ) with an excess of air, so that a portion of the in the at least one second cylinder ( 3 ) admitted air with the combustion exhaust gas in the catalyst ( 6 ). Engine system with a control unit according to claim 9 and an internal combustion engine ( 2 ) with several cylinders ( 3 ), whereby the cylinders ( 3 ) each an injection valve ( 7 ) for injecting fuel into the plurality of cylinders ( 3 ) of the internal combustion engine and intake valves for introducing air into the cylinders ( 3 ) to an air-fuel mixture in the cylinders ( 3 ) to provide a drive torque, wherein a catalyst ( 6 ) is provided via the combustion exhaust gas from the cylinders ( 3 ) is discharged.

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